1. Field of the Invention
The invention relates to gas-turbine systems having two combustion chambers which are arranged in succession and are connected to a high-pressure turbine and a low-pressure turbine respectively.
2. Discussion of Background
An important aim of development in the power station sector is to increase the thermal efficiency. This aim can be achieved in both pure gas-turbine power stations and so-called combined power stations consisting of gas and steam turbines by improving the thermodynamic gas-turbine process.
CH-A-273 506 discloses a gas-turbine system which essentially consists of a first combustion chamber, a high-pressure turbine connected to the first combustion chamber, a second combustion chamber arranged downstream, and a low-pressure turbine connected to the latter. The exhaust gases of the first combustion chamber, after their expansion in the high-pressure turbine, are directed into the second combustion chamber, are heated again there by admixture of fuel, and are expanded again in the low-pressure turbine. Thus the thermal efficiency or else the actual power output is increased compared with gas turbines having only one combustion chamber.
However, more recent developments are directed toward increasing the pressure ratio in the high-pressure turbine and the inlet temperature of the exhaust gases directed into the second combustion chamber above hitherto conventional values. The known systems are not equipped for loads of this type. On account of the substantially higher inlet temperatures, a clear increase in the NOx-emissions would occur in the gas turbines used hitherto. In addition, a correspondingly high recovery of kinetic energy of the exhaust gases from the high-pressure turbine is not guaranteed. A further disadvantage of such systems is their relatively large overall length, which results from the arrangement of the second combustion chamber and the low-pressure turbine connected to it. In addition, problems arise with the ignition of the combustion mixture on account of the high velocity of the exhaust gases injected into the second combustion chamber.